The present invention relates to a method and an apparatus for processing wafers, e.g., semiconductor wafers, utilizing a wafer processing disk.
A microchip or integrated circuit formed on a wafer surface must be separated from the wafer surface, which typically contains an array of integrated circuits, and put in a protective package. Semiconductor wafer packaging has traditionally lagged behind wafer fabrication in process sophistication and manufacturing demands. The advent of the VLSI-ULSI era in chip density has forced a radical upgrading of chip packaging technology and production automation. It is a widely held belief in the art that eventually packaging will be the limiting factor on the growth of chip size. Accordingly, much effort is going into new package designs, new material development, and faster and more reliable packaging processes.
It is often necessary to thin wafers in the packaging process because of an industry trend to using thicker wafers in fabrication. This trend presents several problems in the packaging process. Thicker wafers require the more expensive complete saw-through method at die separation. Thicker wafers also require deeper die attach cavities, resulting in a more expensive package. Both of these undesirable results are avoided by thinning the wafers before die separation. It is also often necessary to remove, by wafer thinning, electrical junctions formed inadvertently on the back side of the wafer during fabrication.
Thinning steps generally take place between wafer sort and die separation. Wafers are reduced to a thickness of 0.2-0.5 mm. Thinning is done through mechanical grinding, mechanical polishing, or chemical-mechanical polishing. Wafer thinning or backgrinding has traditionally been a difficult process. In backgrinding there is the concern of scratching the front of the wafer and of wafer breakage. Stresses induced in the wafer by the grinding and polishing processes must be controlled to prevent heat induced wafer and die warping. Frequently, to secure a wafer 22 during a thinning operation, the wafer 22 is secured to a wafer chuck 26 with an adhesive sheet or film 24, see FIG. 10. However, heat generated during the thinning process subjects the adhesive sheet or film 24 to degradation and failure resulting in wafer damage. Accordingly, there is a need for a wafer processing apparatus that minimizes heat induced stress and damage during wafer thinning.
Wafer thinning done through mechanical grinding, mechanical polishing, or chemical-mechanical polishing often requires a plurality of wafer polishing or grinding disks to achieve a desired outcome. For example, it is often necessary to initiate wafer processing with a coarse grinding disk and complete the processing with a fine grinding disk. This requirement leads to corresponding increases in production time and equipment cost. Accordingly, there is a need for a wafer processing method wherein a single processing disk may be utilized where conventional methods utilize a series of processing disks.
These needs are met by the present invention wherein a wafer processing apparatus and method of processing a wafer utilizing a processing slurry are provided.
In accordance with one embodiment of the present invention, a wafer processing disk is provided comprising a processing disk body and a plurality of processing teeth secured to the processing disk body. The plurality of processing teeth project from the disk body to define respective processing surfaces. The plurality of processing teeth include at least one pair of spaced adjacent teeth defining a processing channel there between. The processing channel is shaped such that the cross sectional area of the processing channel decreases as a function of its distance from the processing disk body.
The cross sectional area of the processing channel may decrease continuously or incrementally as a function of its distance from the processing disk body. The cross sectional area of the processing channel may decrease to a zero value. The processing disk body may define a substantially planar tooth mounting surface and the processing teeth may be mounted to the tooth mounting surface. The processing disk body may define a processing fluid passage and include at least one processing fluid port in fluid communication with the fluid passage, wherein the processing fluid port is positioned in the processing channel.
In accordance with another embodiment of the present invention, a wafer processing disk is provided wherein the plurality of processing teeth include at least one pair of spaced adjacent teeth having opposing walls inclined with respect to the processing surfaces such that the opposing walls define a processing channel decreasing in width as a function of its distance from the processing disk body.
In accordance with yet another embodiment of the present invention, a wafer processing disk is provided comprising a plurality of processing teeth wherein at least one of the processing teeth includes a subsurface channel spaced from the processing surface. The subsurface channel may be spaced from the processing surface in the direction of the processing disk body, may be bounded on one side by the disk body, and may extend through opposite sides of the processing tooth. A fluid port may be positioned in the subsurface channel.
In accordance with yet another embodiment of the present invention, a wafer processing disk is provided comprising a plurality of processing teeth, wherein spaced adjacent teeth define a processing channel there between and a fluid port is positioned in the processing channel. The spaced adjacent teeth have opposing walls defining the processing channel between the pair of spaced adjacent teeth. At least one of the opposing walls may follow a curved or inclined path. Preferably, one of the opposing walls follows the curved or inclined path and another of the opposing walls follows a path substantially perpendicular to the processing disk body.
In accordance with yet another embodiment of the present invention, a wafer processing disk is provided comprising a plurality of processing teeth secured to the processing disk body, wherein at least one of the plurality of processing teeth include a fluid via extending from the processing disk body to one of the processing surfaces, and wherein a fluid port is positioned in the fluid via. The fluid via may be bounded at its periphery by the processing tooth and may comprise a bore in the processing tooth.
In accordance with yet another embodiment of the present invention, a wafer processing system is provided comprising a processing disk assembly, a mounted wafer assembly, and a driving assembly. The processing disk assembly includes a processing disk body and a plurality of processing teeth secured to the processing disk body. Each of the plurality of processing teeth project from the disk body to define respective processing surfaces. The driving assembly is coupled to one or both of the processing disk assembly and the mounted wafer assembly and is operative to rotate one of the processing disk assembly and the mounted wafer assembly relative to the other of the processing disk assembly and the mounted wafer assembly. The driving assembly is preferably operative to impart rotary motion to the processing disk body. The driving assembly may further be operative to impart substantially linear reciprocating motion to the processing disk body. The mounted wafer assembly may comprise a wafer secured to a wafer receiving chuck.
In accordance with yet another embodiment of the present invention, a method of processing a wafer surface is provided comprising the steps of: positioning a processing disk adjacent the wafer surface; causing the processing disk to move relative to the wafer surface; distributing a first processing slurry over the wafer surface as the processing disk moves relative to the wafer surface, wherein the first processing slurry comprises a first processing fluid and coarse processing particles, and wherein the coarse processing particles are urged against the wafer surface by the positioning and the movement of the processing disk; and distributing a second processing slurry over the wafer surface as the processing disk moves relative to the wafer surface, wherein the second processing slurry comprises a second processing fluid and fine processing particles, wherein the coarse processing particles are larger than the fine processing particles, and wherein the fine processing particles are urged against the wafer surface by the positioning and the movement of the processing disk.
The method may further comprise the step of distributing a third processing slurry over the wafer surface as the processing disk moves relative to the wafer surface, wherein the third processing slurry is selected from the group consisting of an abrasive slurry and a corrosive slurry. The first processing fluid, the second processing fluid, and the third processing fluid may be substantially identical. The coarse processing particles and the fine processing particles may be mechanically abrasive.
Accordingly, it is an object of the present invention to provide a wafer processing apparatus and a method of processing a wafer utilizing a processing slurry wherein the processing disk is provided with processing teeth designed to improve processing efficiency and wherein the method of processing the wafer utilizes a specially dispensed sequence of processing slurries over the wafer surface. Other objects of the present invention will be apparent in light of the description of the invention embodied herein.